Audit and reduce unstable usage in script

Reasons behind existing unstable features:

alloc:

 - `Rc.make_unique()`
 - `into_raw` / `from_raw` (naming). All over the bindings code.

collections:

 - `Vec.push_all()`
 - `from_str`
   - can be replaced by `.to_owned()`
 - `from_raw_buf`
   - could be done directly

core:

  - `nonzero`
  - `UnsafeCell` (`as_unsafe_cell`)
  - `Zeroable`
  - `Peekable.is_empty`

std_misc:

  - Handle stuff

components/script/dom/storage.rs

@@ -17,13 +17,12 @@ use dom::window::WindowHelpers;
 use util::str::DOMString;
 use page::IterablePage;
 use net_traits::storage_task::{StorageTask, StorageTaskMsg, StorageType};
+use std::borrow::ToOwned;
 use std::sync::mpsc::channel;
 use url::Url;
 
 use script_task::{ScriptTask, ScriptMsg, MainThreadRunnable};
 
-use collections::borrow::ToOwned;
-
 #[dom_struct]
 pub struct Storage {
     reflector_: Reflector,